The correct answer is Cyclin D. This cyclin is expressed throughout the cell cycle, however, it directly regulates the transition from G1 to S phase. Cyclin A is also involved in the G1 to S phase transition and is expressed into the G2 phase. Cyclin E is expressed during the transition from G1 to S phase. Cyclin B is expressed during the transition from G2 to mitosis and regulates this progression. There is no Cyclin F in the cell cycle.

The two main protein types that are crucial to cell cycle regulation are cyclins and CDKs (cyclin-dependent kinases). CDKs are expressed at relatively stable levels at all phases of the cell cycle. Their regulatory partners are cyclins which, as the name suggests, are expressed only when they are needed to help activate a specific CDK and progress the cell to a new phase of the cell cycle. All of the choices are CDKs, and should be expressed during G1 of the cell cycle. Caspases are proteins that are involved in apoptosis. Nucleic acid polymerases would be expected to have elevated activity during S phase of interphase during which DNA is duplicated. 

The contractile ring is made up of actin and myosin-2 and is used to initiate cytokinesis. Polar and kinetochore microtubules have important functions during earlier stages of mitosis. Polar microtubules interact within the cytoplasm during metaphase and anaphase, while kinectochore microtubules directly attach to chromosome centromeres to facilitate separation. Dyenin is a motor protein that interacts with microtubules to aid in protein transport.

During mitosis, sister chromatids will line up in the center of the cell so that they may be pulled to opposite ends by the spindle fibers. This lining up takes place in the second phase of mitosis: metaphase.

Cyclin proteins fluctuate in level during the different stages of the cell cycle (except for Cyclin D). For example, Cyclin E regulates the entry into S phase. The expression of the cyclin E gene increases, which leads to higher Cyclin E protein levels in the cell. After the cell passes S phase, Cyclin E protein is actively destroyed by ubiquitination. 

When Cyclins are bound to Cdks, they can regulate the activity of proteins that regulate processes like replication and microtubule formation; however, of the cellular processes listed, blocking ubiquitination would be the only process that would directly interfere with cyclins' role to regulate the cell cycle as cyclin proteins need to be destroyed at the correct time to allow the cell cycle to progress.

Kinases are proteins that phosphorylate their substrates, often activating these substrates. In the context of cell cycle progression, cyclins interact with cyclin-dependent kinases (CDKs) and activate the CDK kinase domain to phosphorylate substrates and promote cell cycle progression. CDK inhibitors interact with CDKs to inhibit the CDK kinase domain from phosphorylating substrates. 

The correct answer is prometaphase, in which the nuclear membrane dissolves and the microtubules attach to the centromeres. Interphase occurs before mitosis begins, and includes S phase, where the chromosomes are duplicated. In anaphase, the chromosome duplicates are separated by the microtubules. In telophase, cell division begins with the newly separated chromosome copies.

The correct answer is myosin and actin filaments. Myosin hydrolyzes adenosine triphosphate (ATP) and moves along the actin filaments previously assembled at the cell cortex, constricting the actin and the plasma membrane. Lamin is found in the nucleus and gives structural support to the nuclear membrane. Tubulin and microtubules are components of the cell cytoskeleton. 

DNA ligase is an enzyme used to link DNA via the formation of a phosphodiester bond. During lagging strand synthesis, DNA ligase connects the okazaki fragments. Without this enzyme functioning properly, the lagging strand would not be completed.

This question is a little tricky and depends entirely on the definition of when something is officially a chromosome. A sister chromatid is not officially considered a chromosome until being separated from its partner.

During metaphase I, the homologous chromosomes have yet to separate, so ploidy is still 2n (diploid). Statement IV is false.

During telophase I, the homologous chromosomes have separated and the nuclear envelopes have reformed, effectively forming two haploid nuclei during telophase I. Statement I is true.

During metaphase II, the sister chromatids are still attached, so the cells are still haploid. Statement II is true.

During anaphase II, however, immediately after the sister chromatids are separated they are now considered individual chromosomes. This effectively increases ploidy back to 2n until the nuclear envelopes reform. Statement III is false.